Is vitamin D deficiency influenced by obesity during the first 5 years of life? A cross‐sectional multicenter study

Abstract Evidence on the association of 25‐hydroxyvitamin D (25[OH]D) and obesity during the first 5 years of life is limited in China. The objective of this study was to examine the associations between weight, weight for age z score (ZWAZ), weight for length/height z score (ZWHZ), and body mass index for age z score (ZBMI) and 25(OH)D. This was a large population‐based cross‐sectional multicenter study in which the children aged 0–5 years were recruited from 12 children's healthcare centers by a stratified cluster random‐sampling method in 10 cities of the Jiangsu province, China. The 25(OH)D concentration was determined by ELISA. A total of 5289 children were investigated. For 0–71 months children with obesity and nonobesity, the prevalence of vitamin D deficiency was 36.0% and 29.8%, and the 25(OH)D level was 59.8 and 64.0 nmol/L, respectively, and there were all significant difference. Compared with children with nonobesity, children with obesity had higher risk of vitamin D deficiency (OR [95% CI]: 1.33 [1.02, 1.72], p < .05), and had lower 25(OH)D level (β = −3.84, 95% CI = −7.58, −0.09, p < .05). The results for children aged 24–71 months were similar to those for children aged 0–71 months. However, no significant difference was observed in children aged 0–23 months. Vitamin D deficiency was observed in children with greater adiposity during the first 5 years of life. However, the results mainly came from those in the age group of 2 to 5 years instead of the first 2 years in their lives.


| INTRODUC TI ON
Vitamin D deficiency is highly prevalent and has become a common observation for pediatric population. Our results showed that the median serum 25-hydroxyvitamin D (25[OH]D) concentration was 62.9 nmol/L and 28.9% of the children had vitamin D deficiency among children in the Jiangsu province, China (Fu et al., 2016).
Vitamin D deficiency has been a growing concern in recent years, despite constant efforts to lower its prevalence, it remains a widespread issue not only throughout China, but also worldwide. Of preschoolers, 58% (all 5-6 years of age) from southern Croatia had 25(OH)D levels of <50 nmol/L (Karin et al., 2018). Hypovitaminosis D, defined as serum 25(OH)D concentration <50 nmol/L, was found in 91.1% of the healthy children aged 12-60 months in rural Nepal (Avagyan et al., 2016). Prevalence of vitamin D deficiency was 77% among Jordanian healthy infants (Kassab et al., 2016).
The overall obesity prevalence among Chinese children under 7 years of age from 1986 to 2016 was from 0.91% to 4.2%. In the last adipogenesis, adipocyte differentiation, proliferation and apoptosis, cytokine release, adipose tissue inflammation, oxidative stress, etc. (Abbas, 2017).
Preobesity and obesity in children aged 7-15 years are inversely associated with vitamin D status (Jaksic et al., 2019). The prevalence of vitamin D deficiency (serum 25[OH]D <50 nmol/L) was higher in obese children aged 9-13 years compared to their over-and normal weight counterparts (60.5% vs. 51.6% and 51%, p = .017; Moschonis et al., 2018). Obesity is associated with vitamin D deficiency in Danish children and adolescents aged 6-18 years (Plesner et al., 2018). 25-Hydroxvitamin D concentrations are not lower in 6-to 13-year-old children with obesity (Reinehr et al., 2018). Total vitamin D was negatively correlated with BMI SDS in children (age: 12.8 ± 0.2 years; Corica et al., 2019). The interests of previous studies have mainly evaluated vitamin D status and obesity in school children and adolescents (Corica et al., 2019;Jaksic et al., 2019;Moschonis et al., 2018;Plesner et al., 2018;Reinehr et al., 2018), but data worldwide focusing on the first 5 years of life are lacking, to the best of our knowledge. The aim of this study was to determine possible association between obesity and 25(OH)D in Chinese children during the first 5 years of life.

| Participants and study design
In this study, children were recruited from the Jiangsu province between April 2014 and March 2015. This was a large populationbased cross-sectional multicenter study in which the children aged 0-5 years were recruited from 12 children's healthcare centers in 10 cities of the Jiangsu province, China. The sampling method and inclusion/exclusion criteria were reported in a previous study (Zhao et al., 2020). In brief, Jiangsu province is divided into four districts including Nanjing (between 31°14′ and 32°36′ north latitude), the southern of Jiangsu province (between 31°06′ and 32°2′ north latitude), the northern of Jiangsu province (between 32°34′ and 34°28′ north latitude), and the middle area of Jiangsu province (between 31°41′ and 34°06′ north latitude). From each district, 3-4 sampling children's healthcare centers were randomly drawn. The children with metabolic bone disease or abnormal PTH level were excluded.
The parents of the children were face to face interviewed using structured questionnaires, and birth weight, weight, height, and serum 25(OH)D concentration for the children were measured. The study profile is presented in Figure 1.

| Assessment of demographic and lifestyle factors
The structured questionnaire included the information on the children's and mother's demographic characteristics including gender, age, number of pregnancies, parity, gestational age, delivery mode, birth weight, region of residence, season of survey, and location in Jiangsu province. The lifestyle factors included feeding patterns for infants from birth to 6 months (breast milk, formula milk, or mixed), the dietary intake, vitamin D and calcium supplementation, and physical activity.

| Assessments of dietary intake and physical activity
The parent or caregiver was asked to indicate his or her child's frequency and portion size (grams per times) of each food or food in children aged 0-23 months. Vitamin D deficiency was observed in children with greater adiposity during the first 5 years of life. However, the results mainly came from those in the age group of 2 to 5 years instead of the first 2 years in their lives.

K E Y W O R D S
early life, body mass index, children, infant, obesity, vitamin D group in the validated self-administered food frequency questionnaire (FFQ) consumed in the last 1 month prior to the survey. The FFQ was modified on the basis of a previous questionnaire (Lu et al., 2016). Food intake in grams per day was calculated as the reported frequency and portion size. Based on culinary usage or nutrient profiles, we further categorized each food items into 14 food groups as follows: rice and rice products, wheat and wheat products, other cereal products, tubers, starches and starch products, milk and milk products (not including human milk), meat or poultry products, fish and shrimp, eggs, fruits or fruit juices, vegetables, soups, legumes, and oils.
The parent or caregiver was also asked about the children's physical activity levels using a validated self-reported questionnaire, type, and duration of physical activity, especially the time of sleeping and outdoor activity. The questionnaire was modified on the basis of a previous questionnaire (Lee et al., 2017). The physical activity levels were measured as typical hours of daily activity (h/day).

| Definition of terms
The weight for age z score (ZWAZ), weight for length/height z score

| Statistical analysis
The basic characteristics in children with vitamin D deficiency and obesity were described as number (percentage). The basic characteristics in children with 25(OH)D level were described as median P50 (P25-P75). Mann-Whitney U nonparametric test or K independent samples median nonparametric test was used to describe median differences by continuous variables and chi-square test was used to examine differences in categorical variables. Because the first 1000 days of life, that is, the time from mother's conception to child's 2 years of age, can significantly affect the health of children (

| Ethical consideration
The study protocol was approved by the institutional review board of the First Affiliated Hospital of Nanjing Medical University. The approval number is removed for blind peer review.

Ref.
Note: Model 1: Sex, number of pregnancies, parity, birth weight, region of residence, season, and location in Jiangsu province. Model 2: Model 1 + vitamin D supplementation for infants from birth to 6 months, initial time of vitamin D supplementation after birth, and vitamin D and calcium supplementation for children in the last 3 months. Model 3: Model 1 + daily intake of milk, meat, and egg for children. Model 4: Model 1 + time of sleeping and outdoor activity every day for children.

TA B L E 4
The unadjusted and adjusted associations between obesity with vitamin D deficiency and the level of 25(OH)D, respectively, during the first 5 years of life (odds ratios, β coefficients, and 95% confidence intervals) weight, ZWAZ, ZWHZ, and ZBMI in Mainland China. However, no association was observed in 0-23 months children. Due to the rapid growth from 0 to 23 months period, we speculate that this relationship from 0 to 71 months mainly depends on the results from 24 to 71 months. The conclusions of this study are novel.
The results in Table 1 showed that factors such as (Hasan et al., 2017;María et al., 2018).
Further epidemiological and also basic molecular studies in animal models and human biopsies would help to address those issues.
The strengths of our study are as follows. First, data of the association between vitamin D deficiencies with obesity worldwide focusing on the early life cycle from birth to 5 years are lacking, to the best of our knowledge. Second, this was large multicenter crosssectional study. Finally, the study had considered the potential confounding variables including demographic characteristics, dietary intake, vitamin D and calcium supplementation, and physical activity in children.
Nevertheless, the limitations were worth mentioning. First, we cannot infer causality between 25(OH)D and obesity due to crosssectional design of the study. Second, the various forms of vitamin D such as 25(OH)D 3 and 25(OH)D 2 were unable to be distinguished.
Finally, in this study, we used the children's BMI as the indicator of anthropometric status, and future studies should observe the association between body composition (lean mass and fat mass) and the type of the distribution of fat mass (visceral vs. subcutaneous) and 25(OH)D levels using more precise measures of adiposity.

| CON CLUS ION
Vitamin D deficiency was observed in children with greater adiposity during the first 5 years of life. However, the results mainly came from those in the age group of 2-5 years instead of the first 2 years in their lives.

AUTH O R CO NTR I B UTI O N S
RQ and YZ designed the study. HH, HL, KY, YW, WZ, HQ, YN, LZ, GY, GL, and AW collected the data. YZ conducted the statistical analysis and interpretation and drafted the manuscript. RQ revised the manuscript. All authors were involved in the writing of the manuscript and had final approval of the submitted and published versions.

ACK N OWLED G M ENTS
The team of investigators thanks all of the doctors, parents, and children at the participating institutions.

This work was funded by the construction fund for Young Scholars
Fostering Fund of the First Affiliated Hospital of Nanjing Medical University (PY2021050) and Key subjects of women and children of Jiangsu province (FXK201203).

CO N FLI C T O F I NTE R E S T
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the study reported in this article.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data are available on request from the corresponding author.

E TH I C A L A PPROVA L
The study protocol was approved by the institutional review board of the First Affiliated Hospital of Nanjing Medical University (2014-SR-167).